Offshore tower apparatus and method

ABSTRACT

A tower suitable for use in offshore well operations and the like including a plurality of sloping jacket legs extending from the bed of the body of water to a position above the surface of the body of water for supporting a platform thereupon. The jacket legs are reinforced by a surrounding shell of diamond patterned cross braces and a plurality of girder rings lying in a plurality of planes normally with the central axis of the tower. The girder rings are supported against deformity by a bicycle spoke reinforcing system at each girder ring level. The method aspects of the invention include constructing the tower in a generally horizontal posture upon a plurality of generally upright columns. The construction steps include forming a plurality of girder rings and erecting the girder rings upon the columns. Jacket legs are connected between adjacent girder rings along the length of the offshore tower and the tower legs are enclosed within an outer shell of cross bracings. The offshore tower, following construction, is launched into a body of water for transportation to a selected marine site by constructing the tower longitudinally upon a rail having one end thereof lying adjacent a sheet pile wall which permits the lower end of the rail to be positioned below the adjacent water level. A floatation system connected to the tower and the wall is removed to permit the base of the tower to be buoyantly lifted from the construction support. The upper portion of the tower rests upon a rail bearing guide bracket which is initially positioned above the water level. The rail bearing guide bracket may be lifted off the rail by an incompressible fluid and the tower slides into the body of water. Alternatively, the tower may be jacked into the water by conventional jacking devices. Upon being erected at an offshore location, conductors may serve in a dual capacity as conductors and piles, or piles may be inserted into skirt pile casings surrounding the base of the tower and driven into the bed of the body of water by a stinger guided by a rotating truss.

United States Patent 91 Koehler June-11, 1974 OFFSHORE TOWER APPARATUSAND METHOD [75] Inventor: Albert M. Koehler, Houston, Tex. [73]Assignee: Brown & Root, Inc., Houston, Tex.

[22] Filed: Mar. 27, 1972 [21] Appl. No: 238,167

Related US. Application Data [62] Division of Ser. No. 30,098, April 20,l970, Pat. No.

Primary ExaminerJacob Shapiro Attorney, Agent, or FirmBurns, Doane,Swecker &;

Mathis 57 ABSTRACT A tower suitable for use in offshore well operationsand the like including a plurality of sloping jacket legs extending fromthe bed of the body of water to a position above the surface of the bodyof waterfor supporting a platform thereupon. The jacket legs arereinforced by a surrounding shell of diamond patterned cross braces anda plurality of girder rings lying in a Marshall 6l/53.5 X

plurality of planes normally with the central axis of the tower. Thegirder rings are supported against deformity by a bicycle spokereinforcing system at each girder ring level.

The method aspects of the invention include constructing the tower in agenerally horizontal posture upon a plurality of generally uprightcolumns.

The construction steps include forming a plurality of girder rings anderecting the girder rings upon the columns. Jacket legs are connectedbetween adjacent girder rings along the length of the offshore tower andthe towerlegs are enclosed within an outer shell of cross bracings. Theoffshore tower, following construction, is launched into a body of waterfor transportation to a selected marine site by constructing the towerlongitudinally upon a rail having one end thereof lying adjacent a sheetpile wall which permits the lower end of the rail to be positioned belowthe adjacent water level. A floatation system connected to the tower andthe wall is removed to permit the base of the tower to be buoyantlyliftedfrom the construction support. The upper portion of the towerrests upon a rail bearing guide bracket which is initially positionedabove the water level. The rail bearing guide bracket may be lifted offthe rail by an incompressible fluid and the tower slides into the bodyof water. Alternatively, the

tower may be jacked into the water by conventional jacking devices. Uponbeing erected at an offshore location, conductors may serve in a dualcapacity as conductors and piles, or piles may be inserted into skirtpile casings surrounding the base of the tower and'driven into the bedof the body of water by a stinger guided by a rotating truss.

5 Claims, 41 Drawing Figures PATENTEBJUH 1 1 I974 3 L 8 15B 7 l SHEEI'01.- OF 10 aim.

PATENTED HH m4 3815371 sum '02 or10 FIG]:

PATENTEDJUH H 1914 3815371 SHEET 03 0F 10 PATENTEDJUM 1 1 .974

saw on or 1o PAYENTEQJUN 1 1 m4 SHEET 05 0F 10.

PATENTEDJUM 1 1 1914 3315371 sum '06 or 10 PATENTED UH 1 1 m4 3J8 1 51371 sum 08 or 10 PATENTEDJUH 1 1 1914 31815371 saw as or 10 1 a ItOFFSHORE TOWER APPARATUS AND METHOD This is-a division, ofapplication,'Ser. No. 30,098, filed Apr. 20, 1970, now U.S. Pat. No.3,668,876.

BACKGROUND OF THE INVENTION This invention relates to an offshore towerof the type adaptedto be positioned within a body of water such as, forexample, a lake, sea or ocean.

More particularly, the invention relates to an improved offshore tower,method of constructing the offshore tower, method of launching anoffshore tower into a body of water and a method of fixing the offshoretower to the bed of a body of water.

Towershave a multiplicity of applications in a marine environment, suchasfor example supports for radar or sonar stations, light beacons,marine exploration labs and the like. Additionally, offshore towers arefrequently utilized in the oil industry in connection with drilling,producing, storing and distributing operations.

Drilling for oil and gas in formations situated beneath the surface of abody of water has in the recent past become an extremely challenging andimportant segment of activity in the oil industry. In this connection,creative scientists and engineers'have made tremendous strides inconnection with exploration, drilling, producing, storing anddistributing activities in a marine environment often referred to as thelast earth frontier. Notwithstanding the successes of the recent past,however, significant challenges remain in this infant segment of the oilindustry.

In the initial stages of development, offshore tower operations wereconducted in locations of relatively shallow water depths, from a fewfeet to one or two hundred feet, such as exists along the near shoreportions of the Gulf of Mexico. More recently, however, large mineralresources have been detected in water depths ranging from a few hundredto a few thousand or more feet, such as exists along the Pacific Coastcontinental shelf and the Arctic regions.

In order to exploit mineral resources which exist below such substantialdepths of water, tower designs which have been reliable and effectivelyutilized in the past have undergone considerable redesign for prolongedhigh stress deep water use. In this connection, offshore towerspresently being designed are enormous structures presently trulysignificant engineering challenges, not only from an initial designaspect, but from a subsequent construction, transportation and erectionpoint of view.

conventionally, offshore towers are constructed with a plurality ofgenerally upright legs which extend between the bed and the surface ofthe body of water for supporting a platform above the surface of thebody of water. These upright legs are stiffened or reinforced by lateralbrace members or crossing struts. The reinforcement members initiallyrequire accurate cutting operations to form coped ends to intimatelyabut against the circular jacket legs and then require an intricatewelding operation to fixedly connect the bracing to the jacket legs.

While such a structure and technique of fabrication has been generallysatisfactory in the past, significant disadvantages remain. Moreparticularly in dealing with large, heavy structures, it is oftendifficult to provide an exactly coped end portion which will mate with asimilar curved member, particularly in connection with sloping struts.Therefore, excessive welding is often required and in some instances newstruts have to be fabricated. Further, cross braces and struts abuttingagainst the tubular jacket legs tend to punch through the jacket legs orat least deform the jacket legs into a generally eliptical or out ofround configuration. Merely increasing the wall thickness of the jacketlegs is generally unsatisfactory, since the increase in weight of thejacket legs adds significantly to the total weight and cost of theoffshore tower. Further. the legs cannot be adequately reinforced orstiffened internally due to space limitations since the legs frequentlycontain piles, drilling conductors, diver access tubes and the like,which consume the majority of the space in the interior of the tubularleg. Gusset plates and the like have been employed to reinforce theexterior of the legs so that the load transfer takes place across alarger area. However, this indirect transfer causes stressconcentrations which can drastically reduce the fatigue life of thejoint and structure. Further, such additional plates materially add tothe weight of the tower structure, and therefore the overall cost, aspreviously mentioned.

It would therefore be highly desirable to provide a means forreinforcing or stabilizing jacket legs of an offshore tower which wouldtransfer the load through the connection and not into the tower legs.

Further, in at least some instances, it has previously been the practiceto stabilize an offshore tower by forming laterally extending skirt pilecasings about the base of the offshore tower and driving piles, havingapproximately the same diameter as the jacket legs, through the pilecasings and into the bed of the body of water.

In areas, however, where loose bottoms exist or seismic or stronghydrodynamic loads are anticipated, it has been found that suchconventional towers with skirt pile reinforcing have not been totallysatisfactory. In this connection, it would be desirable to provide ajacket piling system which would enhance the capabilities of theoffshore tower to withstand large lateral loads such as produced byshifting earth formations,

etc.

Another difficulty with previously known offshore towers has been thedifficulty in placing piles within the skirt pile casings and thensubsequently driving the piles deeply into the bed of the body of water.In this connection a plurality of pile driving guide collars have beenestablished at the end of cantilever arms extendingalong the lateralsurface of the offshore tower at a plurality of elevations with a stringof axially aligned guides for each pile casing. Therefore, following thedriving of one pile the entire driving string has to be raised insegments and reconstructed in the next string of guides. Such a processis extremely laborious, time consuming and economically undesirable.

It would therefore be desirable to provide a method and apparatus forconveniently guiding the piles into the pile casings and rapidly drivingthe piles deeply into the bed of the body of water without withdrawingthe It has been found, however, that in trying to meet the currentdemand for deep water structures, which typically may be five hundred ortwo thousand or more feet in length. conventional constructiontechniques are often not suitable to fabricate such enormous towers. Inthis connection, shipyard facilities to fabricate these enormousstructures presently do not exist. Moreover,

once fabricated. there remains the substantial problem of transportingthe tower to a body of water for subse quent navigation to a desirablemarine site.

It would therefore be highly desirable to provide a method forfabricating large tower structures of indefinite length and acorresponding means of launching the towers thus constructed into a bodyof water for transport to a desired offshore site.

OBJECTS AND SUMMARY OF THE INVENTION I It is therefore a general objectof the invention to provide a method and apparatus which will obviate orminimize problems of the the type previously de scribed.

It is a particular object of the invention to provide an offshore towerwith a novel cross bracing system which will minimize the stressconcentrations which typically exist between offshore tower jacket legsand stiffening horizontal braces and struts while simultaneouslyminimizing the total tower weight.

It is a further object of the invention to provide an offshore towerwhich will transfer lateral loads through a cross bracing junction andnot into the tower jacket legs.

It is a further object of the invention to provide a method forfabricating an offshore tower which will not be limited by the size ofthe tower required to be constructed. t

tioned within a body of water and resting upon the bed of thebody ofwater with an upper portion thereof extending above the surface forstably supporting a platform with drilling equipment thereupon;

FIG. 2 is a fragmentary corner view of an offshore tower which in fullembodiment would be illustrated identically as in FIG. 1 with theexception that surrounding the bottom portion of the tower, twice asmany jacket legs are provided which extend alternately from the base ofthe tower upwardly and coextend with twice as many cross bracingconnections to a position intermediate the length of the offshore tower;

FIG. 3 is an isometric view of an offshore tower according to theinvention and is provided with a longitudinally extending pile guidingand driving truss circumferentially riding on the outer periphery of thetower and is further provided with a circumferentially extending belt ofjacket pile casings and piles about the base for pinning the offshoretower to the bed of the body of water;

FIG. 4 is an isometric view of a girder ring forming a portion ofthe-invention;

It is a still further object of the invention to provide a stabilizingstructure connected to the base of the offshore tower capable ofwithstanding large lateral loads such as produced by seismicdisturbances.

It is another object of the invention to provide a method and apparatusfor guiding and driving piles into jacket pile casings in a convenientand rapid manner.

method and apparatus for increasing the capacity of a tower to supportdrilling operations in a plurality of locations.

It is still another object of the invention to provide a convenientmanner of fabricating an offshore tower which will maintain thegeometrical integrity of the .offshore tower during the construction andthe subsequent launching operations.

THE DRAWINGS Other objects and advantages of the present invention willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings wherein:

FIG. 1 is an isometric view of an offshore tower, with a lower cornerremoved for illustration: purposes, posi- FIG. 5 is a segmental detailedview of a portion of the girder ring disclosed in FIG. 4;

FIG. 6 is a detailed view of a bracket for connecting the girder ringspokes to the hub of the girder ring;

FIG. 7 is a cross-sectional view of FIG. 6 taken along section line 7-7therein;

FIG. 8 is a detailed segmental view of a portion of a girder ringdisclosing the brackets for connecting the hub spokes with the inner rimof the girder ring;

FIG. 9 is a sectional view of FIG. 8 taken along section line 99therein;

FIG. 10 is a sectional view of FIG. 8 taken along section line l010therein;

FIG. 11 is a segmental view of a section of the outer periphery of anoffshore tower disclosing the relationship of the tower legs, the crossbracing shell and the girder ring;

FIG. 12 is an isometric view of a segment of an offshore towerdisclosing an alternate girder ring configuration;

FIG. 13 is an isometric view of a segment of the outer portion of anoffshore tower disclosing an alternate connection arrangement of thegirder ring disclosed in FIG. 12, with the tower legs and cross bracingshell;

FIG. 14 is an isometric view of a segment of the outer portion of anoffshore tower disclosing a still further alternate girder ringarrangement;

FIG. 15 is an isometric view of a portion of an offshore towerdisclosing an alternate connection configuration of the girderringarrangement disclosed in FIG.

FIG. 16 is a plan view of a unitary cross forming a part of theinvention; FIG. 17 is a top view of the unitary cross disclosed in FIG.16;

FIG. 18 is a plan view of a segment of a skirt piling FIG. 21 is a planview of the bridge shown in FIG. 20; I

FIG. 22 is a sectional view of FIG. 21 taken along section line 2222therein;

FIG. 23 is a detailed elevational view of an alternate connection bridgebetween a tower jacket leg and a horizontally disposed brace spanningadjacent skirt pile casings;

FIG. 24 is a plan view of the bridge shown in FIG. 23;

FIG. 25 is a side elevational view of a pile driving truss asisometrically illustrated in FIG. 3;

FIG. 26 is a side elevational view of the pile driving truss shown inFIG. 25;

FIG. 27 is a cross-sectional view of FIG. 25 taken along section line27-27 therein;

FIG. 28 is a detailed view of the truss driving mechanIsm;

FIG. 29 is a segmental elevational view of a portion of the verticalcolumns utilized to hold the girder rings during the tower constructionoperation;

FIG. 30 is a detailed view of an upper portion of one of the' supportcolumns shown in FIG. 29 specifically illustrating the-adjustable upperbracket and pillow blocks;

FIG. 31 is a side elevational view of FIG. 30;

FIG. 32 is a cross-sectional view of FIG. 31 taken along section line32-32 therein;

FIG. 33 is a schematic elevational view of an offshore tower in apartially completed stateof construction;

FIG. 34 is a plan view of an offshore tower positioned within aconstruction bay adjacent a body of water;

FIG. 35 is an end elevational view of the base of the tower asillustrated in FIG. 34, resting upon supporting blocks;

FIG. 36 is an end elevational view of the top of the offshore tower, asillustrated in FIG. 34, resting upon a rail bearing guide;

FIG. 37 is a detailed elevational view of the rail bearing guide; I

FIG. 38 is a sectional view of the rail bearing guide of FIG. 37 andtaken along section line 38-38 therein; and

FIGS. 39+4l disclose in a sequential schematic array a method oflaunching the previously constructed offshore tower along the monorailof the-construction bay and into the body of water for transport to adesired marine site.

DETAILED DESCRIPTION General Structure Referring now to the drawings,and more particularly to FIG. 1 thereof, there will be seen an offshoretower 50 situated upon the bed 52 of a body of water 54 and extendingabove the surface 56 of the body of water for stably supporting aplatform 58 thereabove. The body of water 54 typically may range from200 to 2,000 or more feet in depth. The offshore tower, as previouslymentioned, may be used for a multiplicity of applications such as, forexample, a support for radar stations, light beacons, marine explorationlabs and the like. More predominantly, however, offshore towers of thetype illustrated are utilized in the oil industry for drilling,producing, storing and distributing operations.

In this connection, the platform 58 frequently is composed of at leasttwo decks, a main deck 60 and a cellar deck (not shown) positionedtherebelow. The main deck may serve to support a plurality of drillingrigs 62 which progressively and simultaneously drill in a plurality oflocations around the periphery of the offshoretower. Further, the maindeck may be provided with a plurality of cranes and various mud tanksand other equipment suitable for sustaining a continuous drillingoperation. The cellar deck typically may contain housing units,generators, compressors, control centers, test facilities and the like.Tower Structure The offshore tower 50 is composed of a plurality ofjacket legs 64 disposed symmetrically about a central vertical axis 66and forming an outer tower surface generally in the geometricalconfiguration of a truncated cone. The peripherally disposed uprightjacket legs 64 are supportingly interconnected by a diamond patternedshell of cross bracings 68 which serve to take lateral loads imposedupon the offshore tower 50. It will be appreciated by those skilled inthe art that the diamond patterned shell of cross bracings shown in FIG.l in a preferred outer encompasing posture may in some instances beplaced within the interior of the inner tower peripher formed by thejacket legs 64. Sur-' rounding the upright jacket legs 64 and thesurrounding shell of cross bracings 68 are a plurality of girder rings70 positioned around the outer periphery of the tower.

I The girder rings 70 lie in a plurality of mutually parallel planes alllying normally to the central tower axis 66.

As will be readily realized by viewing FIG. 1, the girder rings 70incrementally diminish in diameter from the base 72 of the offshoretower to the top 74 thereof. Each of the girder rings 70 is supportedagainst out of round deformation by a bicycle bracingnetwork 76 (noteFIG. 4) which will be more fully described hereinafter.

The upright jacket legs 64 are columnar structures and are sufficientlydimensioned to receive concentrically within the interior thereof aconductor 78 which is driven into the bed of the body of water 52. Theconductor may be grouted to the interior of the jacket leg and serves toguide a drilling string (not shown) for drilling throughthe jacket legsinto formations positioned beneath the offshore tower 50. Moreover theconductors serve the at least two additional significant purposes ofstrengthening and supporting the tower.

As illustrated in FIG. 1, it may be desirable in some instances to drillin locations between adjacent jacket legs. In this connection, conductorstrings 80 shown by dotted lines may be guided through a plurality ofaxially aligned conventional funnel shaped collars 82 (not FIG. 8)fixedly connected to the girder rings 70.

In those instances where additional lateral stability is desired, thebase 72 of the offshore tower may be provided with a tighter shell ofcross bracing struts 86 identical in general configuration with thecross bracing shell 68. The spacial area, however, within an individualdiamond is diminished by a factor of four while there are twice as manycrossing junctions at a given planar level. The lateral structuralstrength of the offshore tower is thereby significantly increased.

Referring now to FIG. 2, there will be seen a lower corner segmentalview of an offshore tower 87, the remainder of which being substantiallyidentical with the tower as disclosed in FIG. 1. Tower 87 includes aplurality of jacket legs 88 extending about the periphery of the towerand containing therein conductors 90, p

which extend coaxially within the jacket legs and deeply into the bed ofthe body of water. .Drilling strings are then lowered through theconductors 90 for drilling earth formations situated beneath theoffshore tower.

The-conductor legs 80 are surrounded by a cross bracing shell 92 andgirderrings 94, identically as described in connection with the towerillustrated in FIG.

The offshore tower 87 illustrated in FIG. 2, however, in addition to thestructure of FIG. 1, is provided with a plurality of jacket legs 96which extend between the bed of the body of water, upwardly only apartial distance along the offshore tower lateral surface. Above thejacket legs 96, conventional conductor guide collars 82 (note FIG. 4)are positioned within the girder rings94 in a manner previouslydiscussed. The lower jacket leg segments 96 serve to isolate the lowerportion. of the conductor strings from excessive compressive forces andcurrent stresses which may be produced when the base of the tower ispositioned in relatively deep water. Further, it will be seen thatadditional cross bracings 95 extend from the leg of the body of waterupwardly and coextensively with the jacket legs 96 to increase thelateral structural strength of the offshore tower and distribute loadsto the conductor piles.

ally about the circumference thereof. The pile guides 108 are fixedlyinterconnected with each other by horizontally disposed braces 110 andsloping struts 112. Piles 114 are guided within the skirt pile guides108 and are driven into the'bed 52 of the body of water 54 byutilization of a rotating truss 116 connected along the periphery of theoffshore tower 97 which will be more fully described hereinafter.

Girder Ring Segment w v The truncated cone offshore towers 50, 87 and97, as isometrically illustrated in FIGS. 1-3, all utilize a pluralityof girder rings.

As specifically illustrated in FIG. 4, a girder ring l18 is constructedwith a circular outer beam 120 and a coaxially disposed circular innerbeam 122. The beams are interconnected by sloping braces 124 in a mannerwhich will be more specifically disclosed hereinafter.

The girder ring is supported against out of round deformation by abicycle bracing system 76 comprising an axially disposed tubular hub 126having an upper flange plate 128 and a lower flange'plate 130 disposedcircumferentially about the outer periphery of tubular hub 126.Emanating from the upper flange plate 128 and the lower flange plate 130are a plurality of spokes 132. These spokes may be composed, forexample, of a set of steel wires wrapped with a surrounding cloth with aresin covering to prevent excessive corrosion thereof. r

The spokes 132 emanate from both the upper and lower surface of both theupper flange plate 128 and the lower flange plate 130. At each junctionlocation of the spokes 132 with the inner beam 122 of the girder ring118, one spoke originates from the upper flange plate 128 and a secondspoke emanates from the lower flange plate 130.

A segment of spoke junction locationshave been labelled in the topportion of FIG. 4 as junction points A through E. The spoke lines havebeen hatched in coding to more fully illustrate the connection system.In this connection, reference may be had to the legend at the lowercorner of FIG. 4, wherein the full dotted line indicates a spokeemanating from the lower flange lower side L.F.L.S.). The dashed anddotted line indicates a spoke from the upper flange lower side(U.'F.L.'S.).. Spokes radiating from these flange locationswill be seenas connecting with the beam 122 at position A. In the next clockwiseconnection B, there will be seen a solid line emanating from the upperflange which, as noted in the legend, represents the upper flange upperside (U.F.U.S.), while the long dash line represents the lower flangeupper side (L.F.U.S.).

Position C on the rim then is provided with spokes (note line coding)from the lower flange lower side and the upper flange lower side. Atposition D, spokes emanate from the upper flange upper side andlower'flange upper side. Thus, in alternate locations around theperiphery of the girder ring 118 the spokes emanate from The bracketattachments 136 may be formed from.

one of a number of conventional designs currently utilized inconjunctionwith prestressing operations.- One specific embodiment,however, that is satisfactory, is specifically illustrated in FIGS. 6and 7. The bracket arrangement 136, as specifically there illustrated,is composed of a base plate 138 and a plurality of normally extendinglegs 140.-A head section 142 interconnects the vertical legs andthe'ba'se plate. The head section 142 is provided with a pair ofchannels 144 which open upwardly and serve to receive in sliding fashiona flexible wire or braided bundle of strands 134. .luxtaposed againstthe head section 142 of the bracket 136 are one or more key plates 146having a pair of downwardly facing channels 148 fashioned therein andbeing dimensioned to spacially conform with the upward channels 144 inthe head. plate 142 as specifically illustrated in FIG. 7. The wires 134are formed with integral head beads 150 and are spaced from the keyplate 146 by one or more circular bushing rings 152. The key plate 146in conjunction with the juxtaposed head plate 142 serves to confine theends of the prestressed bundle of wires 134.

Referring now to FIG. 8, there will be seen a segmental plan view of thegirder ring.l18 including an outer beam 120 and an inner beam 122. Thebeams are spaced, as previously mentioned, by a plurality of slop-.

ing supports '124positioned therebetween about their periphery. Further,there will be seen a junction localel channels 156 for the reception ofwires 134. A key plate 158 is provided with a pair of inwardly extendingcompatibly dimensioned channels 160 which serve to retain wire head tabs162 within the channels 156, in a manner previously discussed inconnection with FIGS. 6 and 7.

Following the connection operation, the individual wires or bundles ofbraided wire strands 134 are prestressed by conventional hydraulicstressing devices (not shown), and a suitable number of key plates 158or 146 may be inserted to retain the wire in the desired tension. Itwill be readily recognized that such a tensioned spoke system willmaintain the girder ring in an approximately circular posture.

Peripheral Tower Elements Referring now to FIG. 11, there will be seenan isometric segmental view of a preferred embodiment of ring girder 118and its manner of connection to a plurality of jacket legs 164 anddiamond patterned cross bracings 166.

The ring girder 118 is composed of an inner-T-beam rim 122 and an outerT-beam rim 120, having the long legs 168 thereof mutually facing eachother and being rigidly interconnected by a plurality of sloping braces124. The braces 124 may be either straps or tubular stock, as preferredor as load requirements dictate. The jacket legs 164 and cross braces166 are positioned between the inner and outer girder rims and arefixedly connected to the inwardly projecting legs 168 through one ormore coped notches 170, fashioned therein as required and one or morehorizontal and vertical tying brackets 172 (note also FIG. 9). I

Although mutually facing inner and outer T-beam rims 120 and 122 arepreferred, alternate ring girder structures may be utilized, asspecifically illustrated in FIGS. 12-13 and 1445.

In the embodiment illustrated in FIGS. 12 and 13, there will be seen afirst alternate embodiment having an outer rim 174 formed from a pair ofT-beam members 176 interconnected by slanting braces 178 and an innerrim 180 formed from a pair of angles 182. The T- beams 176 and angles182, respectively, are interconnected by a plurality of bracing straps184. Both the inner and outer rims 180 and 174 are positioned out sideof the jacket legs 164 and diagonal cross bracings 166. Interconnectionbetween the ring girder 118 and the jacket legs 164 and the diagonalbracings 166 may be provided by the provision of bridge members 186,extending from the angle members 182 having coped ends 188 to unite, asby welding, integrally with the jacket legs 164 and across bracingmembers 166.

A second alternate embodiment of the ring girder 118 is illustrated inFIGS. 14 and 15. There will be seen an outer rim 189 formed from a pairof spaced T-beam members 190. An inner rim 192 is formed from a pair ofspaced angle members 194. The angles 194 of. the inner rim 192 and theT-beams 190 of the outer rim 188 are fixedly interconnected by aplurality of sloping struts 196. The outer rim 189 is interconnectedwith the inner rim 192 by a plurality of brace straps 198. Jacket legs164 and cross braces 166 of an offshore tower are extended between theinner and outer rim members and intimately abut coped projections 200,which extend from the rim segments for uniting contact therewith, suchas by welding. Cross Bracing Reinforcing Shell As previously mentionedin connection with FIGS. 1-3, the outer tower structure assumes thegeneral geometric configuration of a truncated cone having jacket legsextending about the outer periphery thereof in a symmetric posture abouta central axis of the offshore tower. The jacket legs arefixedly'interconnected by a cross'bracing network 66 (note particularlyFIG. 1).

Referring again now to FIG. 11, there will be seen a detailed view of asegment of the outer tower periphery including jacket leg segments 164and cross bracings 166, fixedly connected thereto. The cross bracingstruts 166 are integrally joined, as by welding, at their junctionlocations by generally hollow unitary crosses 202. The crosses 202 arefixedly connected at the mid points by bridging structures 172 havingcoped ends, as previously mentioned, to the outer periphery of thejacket legs 164.

Referring now specifically to FIGS. 16 and 17, there will be seendetailed views of the unitary cross 202.

The cross is composed of four arms 204, 206, 208 and 210 of uniformlengths and as best illustrated in FIG. 17 are composed of generallyhollow tubular members. The outer ends 212 are formed with normalsurfaces relative to the axis' of each arm and serve to abuttingly matewith a similar surface of the strut braces 166. This normal abuttingsurface contact provides a convenient welding junction and serves touniformly transmit loads through the junction equally around theperiphery of the junction. The entire crossing structure preferably isfabricated as a unitary piece such as by forgingor casting or in thealternative the inner ends of the legs-may be integrally united as bywelding.

An angle is formed between adjacent legs with opposing angles alpha, A,and beta, B, being equal. The magnitude of these angles will bedetermined by the desired slope of the cross bracing arms 166.

Referring now to FIG. 17, the arms 204 and 210 have axes lying insubstantially the same plane 214 and arms 206 and 208 have axes lying insubstantially the same plane 216. Both of these planes are slightlyangled by an amount rho, P, with respect toa plane 218, which liestangent .to the outer. periphery of the offshore tower. This slightangle permits the cross 202 to conform to the outer periphery of thecurvilinear tower surface.

The unitary cross 202 is equally dimensioned throughout the entirejacket structure including angles alpha, beta and rho. It will bereadily realized that this unitary cross uniformly positioned throughoutthe outer surface of the tower will transmit axial loads through thejunction locations, as opposed to the previously known technique oftransmitting the loads into the tower jacket legs 164. Further, theuniform nature of the cross permits mass assembly techniques whichmaterially reduces the time and labor involved in constructing the crossbracing system. Skirt Pile Guides In instances where the offshore towerwill be situated upon a soft bottom, or the tower must withstand largehydrodynamic or seismic loads, it will be desirable to form a belt ofskirt pile guides 108 around the outer periphery of the base of thetower 106. Piles 114 are 7 driven within the guides 108 for pinning theoffshore structure to the bed of the body of water (note FIG. 3).

Referring now to FIG. 18, there will be seen a top sectional view of asegment of a skirt pile guide structure 220. A plurality of skirt pileguides 108 are horizontally connected by upper and lower tubular bracesegments 1 l0.

As best illustrated in FIGS. 18 and 19, the skirt pile casings 108 areintegrally attached to adjacent jacket legs: 100 by longitudinallyextending diamond patterned bracings 222, which slopingly connectbetween the jacket legs 100 and the skirt pile casings 108.

Cross bracing struts I66 abut against and are weldingly connected tobridge members 224, as shown in FIG. 18 but more specificallyillustrated in FIGS. 20-22.

The bridge 224 is composed of a pair of horizontal 226 and vertical 228plates fixedly interconnected with a crossing plate 230. .The horizontalplates 226 have coped surfaces 232 and the vertical plates 228 havecoped ends 234 to intimately abut with the adjacent jacket leg 100 andskirt piling brace 110 for fixed interconnection therewith, as bywelding.

In those instances where the cross bracing arms 166 do not join at theconnection point between the upper and lower horizontal brace arms 110and the jacket legs 100, an I-beam 236, as generally illustrated in FIG.18 and more specifically illustrated in FIGS. 23 and 24, is providedwhich connects between the upper and lower horizontal braces 110 and thejacket legs 100. The l-beams 236 are provided with coped upper and lowersurfaces 238 and coped web surfaces 240 for intimately contacting theadjacent jacket leg 100 and cross brace 110 for being fixedly weldedthereto to unite the pile brace and jacket legs.

' It will be noted by referring to FIG. l8that the cross sectionaldimensions of the skirt pile legs are significantly larger than thecross-sectional dimensions of the ing may withstand significantly largerloads than correspondingconductor piles while at the same time, thejacket legs which must be larger than the conductor piles may bemaintained relatively small through the use of lateral bracing. Theresulting structure is a combination with maximum strength andsimultaneously the long jacket legswith adequate bracing are maintainedwith relatively small dimensions to minimize total structural weight andcosts.

Pile DrivingTruss V In order to position the pile 114 within the pilecasings 108, a pile positioning and driving truss 116 (note particularlyFIG. 3.), is suspended along the lateral surface of an offshore tower.

Referring particularly now to FIGS. 2527, there will be seen detailedviews of the truss 116.

The truss is'formed from three generally mutually parallel legs 242interconnected by a plurality of struts 244 and horizontal braces 246. Aplurality of ring girder rolling supports 248 are connected along thelegs rest upon and roll about the offshore tower ring girders.

Referring now to FIG. 28, there will be seen a detailed view of arolling support 248..

The rolling support 248 comprises a channel faced roller 250 adapted torest upon the upper edge of a T beam 252 forming at least a portion ofthe outer rim of the girder ring. The roller 250 may be driven through agear linkage system which includes a spur gear 254 axially connectedwith the roller 250 and mating with the skirt pile guide 108. The truss116 may then be ad- I vanced about the periphery of the tower until theaxis of the truss is in alignment with the axis of the next skirt pileguide 108. A pile may then be guidingly lowered into the guide and theprocedure repeated circumferentially around the offshore tower.

A driving stinger may then be lowered within the interior of the truss116 for driving the piles 114 into the bed of the body of water.Following the driving operation of one pile, the truss 116 is advancedinto axial alignment with the next succeeding pile and the drivingstinger drives the'pile into the waterbed. This procedure is duplicatedaround the outer periphery of the offshore tower until all of the piles114 are driven deeply within the bed of the body of water. The truss 116may then be removed for subsequent utilization with other offshoretowers. I

It will be appreciated that the rotating truss 116 provides a means forinitially placing and later driving a plurality of piles about the baseof an offshore tower 242 of the truss 116 and are specifically designedto which may be subsequently removed so as not to interfere withsubsequent operations and wherein the piles may be placed and drivenwithout retracting and placing a lengthy pile column with each shiftpile driving location. I

Following'the driving operation, the piles 1 14 may be fixedly connectedto the guides 108 as by grouting the interior thereof in a manner suchas specifically described in a U.S. Hauber et al. Pat. No. 3,315,473,as-.

signed to the assignee of this application. The disclosure of thispatent is hereby incorporated by reference as though set forth atlength. Method of Fabrication As previously mentioned, the subjectoffshore tower maybe constructed in water depths ranging from 200 to2,000 or more feet. The jacket legs are typically two or more feet indiameter. The overall diameter of the base of the tower structure,typically may be three hundred or more feet in diameter, while at thewater line, the diameter may be feet or more. When dealing with suchlarge structures, essentially composed of tubular steel members, theconstruction or fabrication techniquestypically satisfactorily utilizedin shipyards for smaller tower structures are often either economicallyunsatisfactory or physically incapable of performing the constructionoperation.

A preferred method of constructing the above described offshore towercomprises fabricating a plurality 13 of girder ring segments 118, aspreviously'discussed in connection with FIG. 4, in a shipyard.

A plurality of vertically extending columns 270, as illustrated in FIG.29, are then constructed upon a plurality of pilings 272, which extenddeeply into the earth 274 to fixedly support the columns 270. Thecolumns 270 are aligned and correspond in number and spacing to thenumber of tower girder rings required and to normal spacingtherebetween. The height of the columns 270 are designed to beapproximately equal. Positioned at the upper ends thereof are verticallyadjustable supports 276.

The support 276 comprises four upwardly facing outwardly sloping arms278 which connect at their lower ends to -a quadraped base 280comprising four upwardly facing members 282 (note FIG. 32) which areinterconnected by horizontal braces 284. The members 282 are adjustablyconnected to the upper end of a column 270 by connection with fouraxially adjustable hydraulic cylinder and ram assemblies 286. At theupper end of the arms 278 upwardly extending members 288 arelongitudinally connected by braces 290 and serve to support a pair ofspaced I-beams 292 which in turn support a pair of pillow blocks 294.

Asbest illustrated in FIG. 29 the girder rings 1E8 previously assembledare upended and the hubs 126 thereof positioned upon a pair of adjacentpillow blocks 294 of successive columns 270. The pillow blocks 294arethen vertically manipulated until the axes of the hubs 126 are inalignment whereupon the hubs are interconnected by spacer tubes 296 intoa column that extends coaxially about the central tower axis.

The girder rings 118 thus suspended in planes being mutually paralleland normal with the central axis of the tower are interconnected by aplurality of generally normally extending jacket leg segments 164, asspecifically illustrated in FIG. 33.

Following the connection of the jacket leg segments 164, the outer shellof truss bracings 166 and the unitary crosses 202 are formed surroundingand reinforcing the jacket legs.

The process of connecting the leg segments, which are axially aligned toproduce generally hollow legs throughout the tower structure, crossbracings and unitary crosses is duplicated throughout the towerstructure until the tower is completed. Method of Launching Aspreviously mentioned in connection with the fabrication of the offshoretower, current tower designs are often enormous structures. Therefore,not only is it a truly significant problem to initially fabricate thetower, but the manner of launching the tower into a body of water fortransport to the desired site presents a significant challenge.

Referring now to FIG. 34 there will be seen an offshore tower positionedwithin a launching bay 302. The tower 300 may have been fabricated bythe previously discussed technique horizontally upon upright columns270.

In order to launch the tower, a construction bay 302 is first fabricatedalong a shore line where water deep enough to support a large tower ispresent near the shore. The bay 302 is constructed generally normallytoward and into the body of water 306 such that the bay 302 is partiallyon the shore 304 and partially beyond the shore line of the body ofwater 306. The bay 302 is maintained in a dry condition throughout bythe establishment of sheet pile barrier side walls 308 and an end wall309 which permits the lower portion of the tower to be constructed belowthe adjacent water level 306. The columns'270 are positioned along aconcrete rail 310 and the tower 300 is fabricated in a manner previouslydiscussed.

The launching rail 310 is supported upon a plurality of piles 3Mpositioned along the length thereof and driven deeply within the bed 312of the construction bay 302.

Further, in the lower portion of the construction bay, a pair of pads31% are mounted atop a plurality of piles 316 and serve to support bypillow blocks H8 21 pair of floatation vessels 320. The floatationvessels are connected to the outer surface of the offshore tower 300 bya bracing system 322 and an internal framing system 323. At the upperend 324 of the tower 300, a toroidal floatation collar 326 isconstructed which at its lower portionis provided with a rail bearingguide assembly 330, which bears upon and is guided along the rail 310 ina manner which will be more fully described hereinafter. The columns 270are then removed and the tower 300 rests upon a three-point bearingwithin the construction bay.

Referring now to FIGS. 37 and 38, there will be seen detailed views ofthe rail guide and bearing assembly 330. The toroidal floatation collar226 is provided at its lower portion with a support I beam 332 which hasa downwardly projecting leg ending in a cylindrical bearing rod 334. Thebearing rod 334 rests in a freely pivotal manner upon a rail bearingguide 330.

The rail bearing guide 330 is generally triangular in cross-section asbest illustrated in FIG. 38 having a rectangular bottom surface and apillowblock apex 336 for pivotally receiving the cylindrical bearing rod334. Along the lateral edges of the bearing guide 330 are guide arms 338(note FIG. 37) which serve to assist in maintaining the bearing guide330 upon the rail 310.

a generally schematic array a sequential depiction of launching theoffshore tower into a body of water.

Referring now specifically to FIG. 39, the end wall 309 of thefabrication bay 302 is removed and the body of water 306 enters theconstruction bay seeking its own level. The water lifts the base 342 ofthe offshore tower 300 from supporting contact with the pillow blocks318 due to the buoyancy of the pair of floatation vessels 320. It willbe noted that the spaced relationship of the floatation vessels 320provides, 'in cooperation with the bearing 330, a three point bearingarrangement which stably supports the-tower. As the base 342 of theoffshore tower rises, the upper portion of the tower 324 will pivotabout the bearing-rail guide 330.

A source of incompressible fluid 344 is connected I into the interior ofthe bearing guide 330 by a line 346.

incompressible fluid, such as for example water, oil, soap suds or thelike, is then pumped into the chambers formed by the partitions 340. Thebearing rail guide 33b is then lifted from frictional contact with therail be jacked down the rail by conventional jacking de vices. The line346 is of sufficient length to maintain contact with the source 340 andthe bearing guide 330, for-a sufficient. period of time for the tower togain momentum as it descends down the launching rail. When sufficientmomentum isachieved, however. the lubricating fluid is no longernecessary and the line 346 may be severed. Alternately, theincompressible fluid source may be stored within the tower.

. Referring now to FIG. 40, it will be seen that as the tower slidesdown the rail 310, the toroidal floatation collar 326 will come. intocontact with the surface of the body of water 306 and by its buoyancylift the upper portion of the tower 324 off of bearing contact with theguide bearing 330.

Referring to FIG. 41, it will thus be seen that the offshore tower 300may be'completely supported on a floatation system which includes anupper toroidal floatation collar 326 and a pair of spaced floatationvessels 326 connected to the outer periphery of the base of the tower342. The tower 300 may then be towed to a desired offshore site and sunkto the bed of a body of water in a manner more fully disclosed andspecifically claimed in applicants copending US. application, Ser. No.29,831 now US. Pat. No. 3,693,361.

While the specific floatation system utilized in conjunction with thelaunching operation has been described as comprising a toroidal collarand a lower floatation vessel or vessels, it will be realized that otherfloatation systems may be utilized in conjunction with the previouslydescribed launching technique. One such floatation system isspecifically described and claimed in copending US. application, Ser.No. 29,994 now US. Pat. No. 3,633,369 by Joseph Benton Lawrence, saidapplication being of common assignment with the present application.

in those instances where it is desired to utilize this latter'floatationsystem to transport the offshore tower to a desired marine site,-itwill-be recognized by those skilled in theart that the rail bearingguide 330 may be connected directly to an upper brace affixed to theoffshore tower 300 and the articulated string of floatation vessels maybe attached to the lateral surface of the offshore tower and supportedupon pillow blocks substantially similar to pillow blocks 318.

SUMMARY OF THE MAJOR ADVANTAGES It will be appreciated that the abovedisclosed'offshore tower is of universal design which may readily beconstructed for any desired water depth.

Another significant aspect of the tower invention is theshell of crossbracings which join through unitary mass production techniques since thedimensions of the junctions are uniform throughout the tower design.Therefore, fabrication time and labor are minimized.

Another significant aspect of the invention is the provision of largediameter pilings juxtaposed peripherally around the base of the offshoretower to withstand large shear and bending loads while permitting thevery long jacket legs to remain economically slender.

A further significant aspect of the invention is the provision of therotating pile guiding and driving truss which serves to accurately alignand drive aplurality of piles with a minimum amount of time and laborspent in pulling and setting pile strings. I

A further significant advantage of the offshore tower is the readyadaptability of the design to vary the number of drilling locationsabout the periphery by the addition of guide collars and conductorswhich may be pinned generally parallel with existing jacket legs througha plurality of girder rings. In the alternative and where large baseloads are anticipated, jacket legs may be fabricated partially from thebed of the body of water upwardly along the surface of the towercoextensive' with an increased number of cross bracings to add strengthto the base of the tower and to receive conductors within the interiorthereof in a protective manner.

Further, girder rings are positionedthroughout the tower design having aradiating bicycle bracing system which supports the jacket legs and thecross bracings from out of round deformation.

A significant method aspect of the invention is the provision of a novelmethod of fabricating an offshore tower of indefinite size and lengthsuitable to meet the increasing demands for. larger offshore towers.

A further significant aspect of the invention is the manner of launchingthe thus constructed offshore tower within a-body of water fortransportation to an offshore site. In this connection, lifting the baseof the tower and unloading the rail bearing guide permits a smooth andefficient launching operation.

An additional significant advantage is the utilization of the conductorsextending within the jacket legs in the dual function to guide adrilling string and aspilmgs.

While the invention has been described with reference to preferredembodiments, it will be appreciated by thoseskilled in the art thatadditions, deletions, modifications and substitutions, or other changesnot specifically described, may be made which will fall within thepurview of the appended claims.

What is claimed is: i

1. A method of pinning an offshore tower to the bed of a body of water,said tower resting upon the bed of the body of water and having skirtpile casings attached to the outer periphery of the base of the offshoretower,

wherein the method'comprises the steps of:

suspending a truss at a plurality of vertically spaced locations uponthe outer periphery of the offshore tower structure;

rotating the truss, suspended upon the outer periphcry of the offshoretower, about the periphery of the offshore tower;

stopping the truss rotation in discrete increments wherein the truss isaxially aligned with piles inserted within the tower skirt pile casings,and

while the truss is stationary driving the piles inserted within theskirt pile casings into the bed of the body of water by a drivingstinger guided within the truss.

2. A method as'defined in claim 1 and further comprising, following saidstep of suspending, the steps of:

3. A method as defined in claim 2 wherein said steps of rotating thetruss comprise:

driving rolling supports extending between the truss and the outerperiphery of the tower in a plurality of vertical locations upon theouter periphery of the offshore tower.

4. An apparatus for facilitating the pinning of an offshore tower to thebed of a body of water, said tower resting upon the bed of the body ofwater and having skirt pile casings attached to the outer periphery ofthe base of the offshore tower and a plurality of girder ring meansextending in vertically spaced horizontal planes about the outerperiphery of the tower wherein said apparatus comprises:

truss means vertically positionable along the exterior surface of theoffshore tower for guiding piles during positioning of the piles withinthe skirt pile casings and for guiding a pile driving stinger duringdriving of the piles into the bed of a body of water; and plurality ofmobile support means, extending between said truss means and at leastmore than one of the plurality of girder ring means for supporting saidtruss means upon the exterior surface of the offshore tower and forrotating said truss means about the outer periphery of the offshoretower and into axial alignment with the skirt pile casings. 5. Anapparatus as defined in claim 4 wherein said plurality of mobile supportmeans each comprises:

a channel faced roller operable to rest upon the upper edge of acorresponding girder ring;- bridge means extending between said rollerand said truss means for connecting said truss means to said roller; andpower means connected to said bridge means and said roller toselectively rotate said roller and thus selectively rotate said trussmeans about the outer periphery of the offshore tower.

1. A method of pinning an offshore tower to the bed of a body of water,said tower resting upon the bed of the body of water and having skirtpile casings attached to the outer periphery of the base of the offshoretower, wherein the method comprises the steps of: suspending a truss ata plurality of vertically spaced locations upon the outer periphery ofthe offshore tower structure; rotating the truss, suspended upon theouter periphery of the offshore tower, about the periphery of theoffshore tower; stopping the truss rotation in discrete incrementswherein the truSs is axially aligned with piles inserted within thetower skirt pile casings, and while the truss is stationary driving thepiles inserted within the skirt pile casings into the bed of the body ofwater by a driving stinger guided within the truss.
 2. A method asdefined in claim 1 and further comprising, following said step ofsuspending, the steps of: rotating the truss, suspended upon the outerperiphery of the offshore tower about the periphery of the offshoretower; stopping the truss rotation at discrete increments wherein thetruss is axially aligned with the tower skirt pile casings; and whilethe truss is axially aligned with the tower skirt pile casings, guidinga pile into the skirt pile casing.
 3. A method as defined in claim 2wherein said steps of rotating the truss comprise: driving rollingsupports extending between the truss and the outer periphery of thetower in a plurality of vertical locations upon the outer periphery ofthe offshore tower.
 4. An apparatus for facilitating the pinning of anoffshore tower to the bed of a body of water, said tower resting uponthe bed of the body of water and having skirt pile casings attached tothe outer periphery of the base of the offshore tower and a plurality ofgirder ring means extending in vertically spaced horizontal planes aboutthe outer periphery of the tower wherein said apparatus comprises: trussmeans vertically positionable along the exterior surface of the offshoretower for guiding piles during positioning of the piles within the skirtpile casings and for guiding a pile driving stinger during driving ofthe piles into the bed of a body of water; and a plurality of mobilesupport means, extending between said truss means and at least more thanone of the plurality of girder ring means for supporting said trussmeans upon the exterior surface of the offshore tower and for rotatingsaid truss means about the outer periphery of the offshore tower andinto axial alignment with the skirt pile casings.
 5. An apparatus asdefined in claim 4 wherein said plurality of mobile support means eachcomprises: a channel faced roller operable to rest upon the upper edgeof a corresponding girder ring; bridge means extending between saidroller and said truss means for connecting said truss means to saidroller; and power means connected to said bridge means and said rollerto selectively rotate said roller and thus selectively rotate said trussmeans about the outer periphery of the offshore tower.